Pulmonary rehabilitation (PR) with supervised exercise training is a key part of care for patients with chronic lung disease (COPD). Patients can improve their shortness of breath, walking distance and quality of life. However, many patients do not improve their overall fitness. They are too breathless to train at a high enough intensity. In a laboratory training study, patients with COPD improved their overall fitness by using single leg cycling. Despite this knowledge, single leg cycling has not been used clinically. The objective of this project is to use and assess single leg cycling in a clinical setting. Single leg cycling can be incorporated into a clinical service (replacing traditional two legged cycling) as the predominant aerobic training strategy, resulting in improvements in cardio-respiratory fitness (peak oxygen uptake).